<HTML>
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A> 
</CENTER>






<HR>

<H3>pair_style lj/smooth command 
</H3>
<H3>pair_style lj/smooth/cuda command 
</H3>
<H3>pair_style lj/smooth/omp command 
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style lj/smooth Rin Rc 
</PRE>
<UL><LI>Rin = inner cutoff beyond which force smoothing will be applied (distance units)
<LI>Rc = outer cutoff for lj/smooth interactions (distance units) 
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style lj/smooth 8.0 10.0
pair_coeff * * 10.0 1.5
pair_coeff 1 1 20.0 1.3 7.0 9.0 
</PRE>
<P><B>Description:</B>
</P>
<P>Style <I>lj/smooth</I> computes a LJ interaction with a force smoothing
applied between the inner and outer cutoff.
</P>
<CENTER><IMG SRC = "Eqs/pair_lj_smooth.jpg">
</CENTER>
<P>The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
cause the force to vary smoothly from the inner cutoff Rin to the
outer cutoff Rc. 
</P>
<P>At the inner cutoff the force and its 1st derivative
will match the unsmoothed LJ formula.  At the outer cutoff the force
and its 1st derivative will be 0.0.  The inner cutoff cannot be 0.0.
</P>
<P>IMPORTANT NOTE: this force smoothing causes the energy to be
discontinuous both in its values and 1st derivative.  This can lead to
poor energy conservation and may require the use of a thermostat.
Plot the energy and force resulting from this formula via the
<A HREF = "pair_write.html">pair_write</A> command to see the effect.
</P>
<P>The following coefficients must be defined for each pair of atoms
types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
above, or in the data file or restart files read by the
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
commands, or by mixing as described below:
</P>
<UL><LI>epsilon (energy units)
<LI>sigma (distance units)
<LI>innner (distance units)
<LI>outer (distance units) 
</UL>
<P>The last 2 coefficients are optional inner and outer cutoffs.  If not
specified, the global values for Rin and Rc are used.
</P>
<HR>

<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
the same as the corresponding style without the suffix.  They have
been optimized to run faster, depending on your available hardware, as
discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A> of the
manual.  The accelerated styles take the same arguments and should
produce the same results, except for round-off and precision issues.
</P>
<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
packages, respectively.  They are only enabled if LAMMPS was built with
those packages.  See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
section for more info.
</P>
<P>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
switch</A> when you invoke LAMMPS, or you can
use the <A HREF = "suffix.html">suffix</A> command in your input script.
</P>
<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
more instructions on how to use the accelerated styles effectively.
</P>
<HR>

<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
</P>
<P>For atom type pairs I,J and I != J, the epsilon, sigma, Rin
coefficients and the cutoff distance for this pair style can be mixed.
Rin is a cutoff value and is mixed like the cutoff.  The other
coefficients are mixed according to the pair_modify mix option.  The
default mix value is <I>geometric</I>.  See the "pair_modify" command for
details.
</P>
<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
option for the energy of the pair interaction.
</P>
<P>The <A HREF = "pair_modify.html">pair_modify</A> table option is not relevant
for this pair style.
</P>
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
tail option for adding long-range tail corrections to energy and
pressure, since the energy of the pair interaction is smoothed to 0.0
at the cutoff.
</P>
<P>This pair style writes its information to <A HREF = "restart.html">binary restart
files</A>, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file.
</P>
<P>This pair style can only be used via the <I>pair</I> keyword of the
<A HREF = "run_style.html">run_style respa</A> command.  It does not support the
<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
</P>
<HR>

<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "pair_lj_smooth_linear.html">pair
lj/smooth/linear</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
